Mortality Prediction in Chronic Obstructive Pulmonary Disease and Obstructive Sleep Apnea

Background: Overlap syndrome of chronic obstructive pulmonary disease (COPD) and obstructive sleep apnea (OSA) is associated with increased mortality. We aimed to assess all-cause mortality in patients with COPD, OSA, and the overlap syndrome and evaluate which polysomnographic indices—apnea-hypopnea index (AHI) or hypoxemic load measurements—better predict mortality within 10 years.Methods: Adults who underwent polysomnography, spirometry, and bronchodilator response tests between 2000 and 2018 were included and divided into four groups according to the presence of COPD and moderate-to-severe OSA (AHI ³15/h). We estimated mortality using Cox model adjusted for demographic/anthropometric covariates and comorbidities; this was called the clinical model. To evaluate prognostic performance, we compared the concordance index (C-index) between the clinical model and extended models, which incorporated one of the polysomnographic indices—AHI, sleep time spent with SpO2 < 90% (TS90), and mean and lowest SpO2.Results: Among 355 participants, patients with overlap syndrome of COPD and moderate-to-severe OSA had the highest risk of death (adjusted hazard ratio, 3.19; 95% confidence interval, 1.02 to 9.96). The C-indices of the extended models with TS90 (%) and mean SpO2 were significantly higher than that of the clinical model (0.765 vs. 0.737 and 0.756 vs. 0.737, respectively; all P <0.05); however, the C-index of the extended model with AHI was not (0.739 vs. 0.737; P=0.15).Conclusions: All-cause mortality was highest in patients with the overlap syndrome. The measurements of the hypoxemic load, not AHI, better predicted mortality in patients with COPD, OSA, and the overlap syndrome.